A woman attacked by four teenagers who tried to strip off her clothing at a community festival has described the group as ''sick''.

The woman, a 38-year-old mother of three, was at Melbourne’s Hastings foreshore on Saturday night to watch fireworks as part of the Western Port festival when she was set upon in an unlit area.

One of the teenagers grabbed the woman from behind and a second stood in front of her and tried to pull down her pants. The two other teenagers stood behind him, in front of the woman, a police spokesman said.

Police said the four teenagers’ attack on the woman was a frightening public sexual assault.

The woman fought off her attackers and they ran off towards the Pelican Park recreation centre in Marine Parade.

The victim, a 38-year-old from Hastings, said she had been unable to find her friends so decided to watch the fireworks alone shortly before the attack.

She said she had been left feeling violated, insecure and unsafe, despite escaping injury.

"(They're) sick, sick people and I just don't understand how they could get any satisfaction from this," she said.

"They weren't laughing, they were... just very much in a hurry to do what they wanted to do."

She managed to fight off the man on top of her, and he fled with his accomplices.

Police Detective Sergeant Stephen McKenzie said it was possible the offenders had lurked in the poorly lit area waiting until the fireworks started so their attack would go unnoticed.

He said that while there were hundreds of people nearby, most were standing either on the beach or the foreshore.

Police were analysing CCTV footage of the area, and did not believe the men filmed the assault. They may have been drinking before the attack.

"It's a despicable act, it would have been terrifying for her," Detective Sergeant McKenzie said.

"For her to be targeted like that, it's despicable."

All of the attackers are believed to be aged in their mid to late teens. One of them was described as being about 160cm tall, with messy hair and wearing jeans at the time.

The victim was unable to provide more detailed descriptions because she was attacked in the dark.